Production of high pressure gaseous oxygen by low temperature rectification of air



3,500,651 LOW March 17, 1970 R. BECKER PRODUCTION OF HIGH PRESSUREGASEOUS OXYGEN BY TEMPERATURE BECTIFICATION OF AIR 2 Sheets-Sheet 1Filed Jan. 13, 1967 INVENTOR RUDOLF BECKER B '0 ATTORNEY March 17, 1970R. BECKER 3,500,651

PRODUCTION OF HIGH PRESSURE GASEOUS OXYGEN BY Low TEMPERATURERECTIFICATION OF AIR Filed Jan. 13,. 1967 2 Sheets-Sheet z INVENTORRUDOLF BECKER ATTORNEY United States Patent 2,58 Int. Cl. F25j 3/04,5/00 U.S. Cl. 62-13 21 Claims ABSTRACT OF THE DISCLOSURE System forproducing high pressure gaseous oxygen by using a liquid pump to elevatepressure of oxygen, and by using such inlet raw gas pressure inconjunction with either air reheat or separation product reheat thatrelatively low pressure gaseous process streams can be employed tovaporize high pressure liquid oxygen.

This invention relates to the low temperature rectification of air, andin particular, to a process and apparatus for the production of gaseoushigh pressure oxygen, wherein the air is cooled and cleansed inregenerators and fed to a fractionating column; nitrogen is withdrawn atthe head of the fractionating column and warmed in the regeneratorscountercurrently to the air; and liquid oxygen is pumped to the desiredpressure and then vaporized countercurrently to a gaseous processstream.

There are several known processes for the production of gaseous highpressure oxygen. Thus, German Patent No. 1,103,363, for example,discloses a process wherein the liquid oxygen is withdrawn from the lowpressure section of a double column and heated,by being pumped through aheat exchanger countercurrently to a stream which had been previouslywithdrawn from the bottom portion of the high pressure section of thecolumn, and was reheated in regenerators (said stream havingsubstantially the same composition as air). Processes are also knownwherein the gaseous oxygen is produced under normal pressure and thencompressed in the gaseous phase to the desired pressure in pistoncompressors.

Known processes have the disadvantage that they require either the useof expensive high pressure compressors for compressing the gaseousoxygen or, as in the apparatus according to the above-mentioned Germanpatent, the employment of an additional high pressure cycle for thedirect or indirect heating and vaporization of liquid oxygen pumped toan increased pressure.

An object of this invention, therefore, is to provide a more economicalsystem for the production of high pressure oxygen gas.

Upon further study of the specification and claims, other objects andadvantages of the present invention will become apparent.

In the drawings:

FIGURE 1 is a schematic illustration of a preferred embodiment of thisinvention wherein the rectification column is in the form of a singlecolumn.

FIGURE 2 is a schematic illustration of a preferred embodiment of thisinvention wherein the rectification column is in the form of a doublecolumn.

To attain the objects of this invention, a system is provided wherein(a) the air is compressed to such a pressure that it is liquefied in thesump of a single column rectification column in heat exchange withboiling low pressure oxygen; (b) a portion, about 20 to 30%, of thecleansed and cooled air from the regenerators is passed countercurrentlyand reheated in the regenerators, and is then employed for vaporizingcompressed liquid oxygen; and (c) the refrigeration is provided byengine expansion of the enriched nitrogen stream from the top of thecolumn. (In this connection, the term engine expansion refers toexpansion with the production of external work.) Each of steps (a), (b)and (c) contributes to the over-all successful operation of the process,and each one separately leads to an improvement in process economics.

Alternatively, this invention also embraces the use of a double column.In this case, the nitrogen enriched fraction obtained from the air isliquefied in heat exchange with evaporating oxygen. In such a system, itcan also be advantageous to pass, instead of said portion of cleansedand cooled air, a corresponding partial amount of a separation productcountercurrently through the regenerators, warming the same in thismanner, and then employing the heated separation product for vaporizingthe high pressure oxygen.

This invention is thus characterized by the utilization of a lowpressure air separation step in cooperation with steps for theproduction of high pressure gaseous 0 without requiring a highcompression of either the air to be separated or the by-product nitrogenstream. In this connection, for the purposes of this invention, the rawair is generally compressed to from 6 to 20, preferably 9 to 12atmospheres absolute. The air separation step for a single columnrectification column is generally conducted at a pressure of 2 to 9,preferably 3 to 4 atmospheres absolute, and for a double column, apressure of generally 6 to 20, preferably 9 to 12 atmospheres absolutein the high pressure section, and generally a pressure of 1.6 to 7,preferably 2.5 to 3.5 atmospheres absolute in the low pressure section.As for the pressure of the high pressure oxygen product, it is generallyat least about 40 to 300, and preferably in the range of about 50 toatmospheres absolute.

The expansion of the nitrogen leaving the head of a single columnrectifier is advantageously conducted in a turbine which is continuouslyunder full load. The nitrogen exit temperature at the regenerators canbe regulated by adjusting the throttle valve for that portion of cooledand cleansed air branched off the main air stream and recycledcountercurrently through the regenerators, which throttle valve islocated upstream of the rectification column.

By the present invention, it is basically possible for either thepressure of the air or the separation product used for heating, or forvaporizing and heating the oxygen, to be much below the pressure of thehigh pressure oxygen. In those cases, however, wherein the oxygen is tobe heated to a relatively high temperature, e.g., 350 to 400 K.,additional compression of the heating gas before heat exchange with thehigh pressure oxygen has been proven to be advantageous. In the lattercase, the pressure of the heating gas is generally about 6 to 20atmospheres absolute, whereas the air is compressed to the lowerpressure of the said range.

As another feature of this invention, it has proved advantageous, forregulating the oxygen withdrawal rate, to provide a recycle line intothe sump of the rectifier downstream of the pressure-elevating liquidoxygen pump.

The refrigeration energy and thusthe purity of the oxygen can becontrolled by expanding the nitrogen in the turbine, by either manuallyor automatically adjusting the suction throttle valve of a bypass lineor the turbine guide vanes. The output capacity of the oxygen pump canbe regulated when operating with a variable air feed by simplycontrolling the liquid level of oxygen in the rectification column.

In still another feature of this invention, the nitrogen withdrawn fromthe head of the rectifier is used, before 3 eing expanded, for coolingthe main air stream and the ecycle air stream.

A major advantage of this invention resides in the relaive simplicityand inexpensiveness of the apparatus that an be employed to carry outthe process.

Referring now to the drawings in detail, air at a rate f 11,000 Nmfi/h.is compressed in compressor 1' and utroduced into cyclically switchableregenerators 1 at a emperature of 300 K. and a pressure of 10atmospheres bsolute. This air is cooled therein to 107.5 K., therebyreezing out H and CO to form cleansed air. Downtream of the regeneratoroutlet, the cleansed air stream 5 branched at 2, one portion about 76.5%passing through :onduit 3 to the sump of the rectification column 5,while be other portion is recycled via the branch conduit 4, nto theregenerators 1, wherein said other portion is releated to 290 K.

In the sump of the column 5, the air in the coil 6 is ndirectly heatexchanged with the liquid fractionated vxygen product. Thereafter, theair is expanded in exansion valve 7 to the column pressure of 3.3atmosiheres absolute.

The column is operated so that the liquid oxygen c01- ects in the bottom(sump) While the nitrogen-enriched tream is withdrawn as overhead. Thisnitrogen stream is lsed for subcooling the air in a countercurrent heatex- :hanger 8, and is then passed to the expansion turbine 16 'iaconduit 14. Before entering the turbine 16, the nirogen stream is passedthrough countercurrent heat ex- -.hanger 15 for cooling the cleansed airbefore the latter s passed through the sump of the column 5.

The nitrogen enters the turbine 16 at 105 K. and 3 itmospheres absoluteand is expanded to 1.2 atmospheres tbsolute, whereby it is cooled to 86K. Thereupon, the nitrogen is passed through the regeneratorscountercurently to the air to be cooled and cleansed, and leaves heregenerators at a temperature of 290 K. For adusting the entrancetemperature of the nitrogen before :ntering the regenerators, there isprovided a turbine by- )ass line 17 having a valve 18 positionedtherein.

From the sump of column 5, the liquid oxygen, unler a pressure of 3.3atmospheres absolute, flows through he conduit 19 to a pump 20 whichcompresses the oxygen 0 preferably 50-250 atmospheres absolute. Thedegree of iurity of the oxygen is determined by adjusting the re-:rigeration output of the turbine. The liquid level of the xygen in thesump of the column 5 can be varied by by- )ass line 22 provided with avalve 21. This line is branched )if the pressure side of the pump 20 andterminates in he sump of the column.

The oxygen, being under a pressure of 50 atmospheres absolute downstreamof the pump 20, is passed through I countercurrent heat exchanger heatedby warm air. The temperature of the oxygen is thereby increased from [02K. to 276 K. From 11,000 Nm. /h. of air, there are hus obtained 1,325Nm. /h. of high pressure gaseous )xygen.

For vaporizing the oxygen in the heat exchanger 10, 2,580 Nmfi/h. of airare branched off at the cold end of the regenerators 1, at 2, warmedcountercurrently to the air entering the regenerators to a temperatureof 290 K., and passed to the heat exchanger 10 via conduit 9.

The air, at a pressure of 9.6 atmospheres absolute, is

cooled to 106.4" K. in the heat exchanger 10, leaves the heat exchanger10 through conduit 11, and is liquefied in a coil 12 in the sump of thecolumn by indirect heat exchange with liquid oxygen, where it is cooledto a temperature of l04.9 K. After further cooling in the countercurrentheat exchanger 8 by gaseous nitrogen, the air is expanded in expansionvalve 13 before entering column 5.

I and warm the liquid oxygen from the low pressure colof the highpressure column is reheated in the group of regenerators 1 and used byway of line 9 to evaporate umn 5' after compression by the pump 20 tothe desired pressure.

The nitrogen is hereby liquefied and passed by conduits 11' and 31 byway of the countercurrent heat exchanger 8 and expansion device 7 as areflux to the head of the low pressure column. Another part of thereflux is achieved from the head of the high pressure column by way of acontrol valve 32 through the line 31.

The other details of FIGURE 2 are analogous to FIG- URE 'l.

Wherein the airis liquefied in the conduits 6 and 12 by evaporatingoxygen in the sump of the single column.

If it is desired to produce relatively warm oxygen at a temperature of350-400 K., a second compressor 9 may be inserted in conduit 9 of FIGURE1 or in conduit 9' of FIGURE 2, respectively.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting. from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Consequently, such changes and modifications are properly,equitably, and intended to be, within the full range of equivalence ofthe following claims.

What is claimed is:

1. In a low temperature air rectification process for the production ofhigh pressure gaseous oxygen which comprises passing raw air throughregenerators; passing resultant cooled and cleaned air to afractionating column; withdrawing nitrogen enriched stream from the headof the fractionating column; passing the withdrawn nitrogen through theregenerators countercurrently to the passage of the raw air; pumpingliquid oxygen from the fractionating column to a higher pressure, andvaporizing resultant higher pressure liquid oxygen countercurrently to agaseous process stream,

the improvement which comprises compressing said raw air to such apressure in the range of 6-20 atmospheres absolute that said resultantcooled and cleansed air is liquefied in'indirect heat exchange as theheat source in the sump of a single column rectification columnoperating as said fractionating column at 2-9 atmospheres absolute, andbranching a portion of the cleansed and cooled air from the regeneratorscountercurrently back through the regenerators to reheat said cooled andcleansed air, and employing resultant reheated air at 6-20 atmospheresabsolute as said gaseous process stream to vaporize the higher pressureliquid oxygen, said higher pressure being about 40-300 atmospheresabsolute. 2. A process as defined by claim 1 wherein refrigerationlosses are compensated for by engine expanding said nitrogen enrichstream from the said fractionating column.

3. A process as defined by claim 1, wherein the reheated air employedfor heating the higher pressure oxygen is additionally compressed withinthe range of 6-20 atmospheres absolute before heat exchange with theoxygen.

4. A process as defined by claim 1, wherein a portion of oxygenwithdrawn from the sump of the fractionating column is branched otfdownstream of the pumping zone, and .is recycled into said fractionatingcolumn.

5. A process as defined by claim 2, Wherein the nitrogen enriched streamwithdrawn from the head of said fractionating column, before beingengine expanded, is passed in countercurrent heat exchange relationshipwith air being passed to said fractionating column from theregenerators.

6. A process as defined by claim 2, wherein the nitrogen enriched streamWithdrawn from the head of said fractionating column, before beingengine expanded, is passed in countercurrent heat exchange relationshipwith reheated air after said reheated air is employed for vaporizing thehigher pressure oxygen.

7. A process as defined by claim 2, wherein the nitrogen enriched streamfrom the head of said fractionating column, before being engineexpanded, is passed in countercurrent heat exchange relationship with(a) air being passed fro mthe regenerators to said fractionating column,and (b) reheated air after said reheated air is employed for vaporizingthe high pressure oxygen.

8. In a low temperature air rectification process for the production ofhigh pressure gaseous oxygen which comprises passing raw air throughregenerators, passing resultant cooled and cleansed air to afractionating column; withdrawing nitrogen enriched stream from the headof the fractionating column; passing the withdrawn nitrogen through theregenerators countercurrentiy to the passage of the raw air; pumpingliquid oxygen from the fractionating column to a higher pressure, andvaporizing resultant higher pressure liquid oxygen countercurrently to agaseous process stream,

the improvement which comprises passing a gaseous process stream, at6-20 atmospheres absolute, said stream being selected from the groupconsisting of (a) branched, cleansed and cooled air from theregenerators, and (b) fractionation product from said fractionatingcolumn, countercurrently through the regenerators to reheat said gaseousprocess stream, and employing resultant reheated gaseous process streamat 6-20 atmospheres absolute to vaporize by indirect heat exchangecontact the higher pressure liquid oxygen, said higher pressure being40300 atmospheres absolute.

9. A process as defined by claim 8, wherein the fractionating column isa double column, and nitrogen enriched gas from the high pressure stageof the double column after being reheated is at least partly liquefiedin heat exchange relationship with evaporating oxygen.

10. Apparatus for producing high pressure gaseous oxygen comprisingreversible regenerators (1) including means for alternate chargingthereof with air and fractionation products;

a compressor for compressing raw air to between 6 and 20 atmospheresabsolute;

a fractionating column (5);

first conduits (3) communicating cleansed and cooled air from saidregenerator (1) to said column (5);

a second conduit (4) communicative with each of said first conduits (3)downstream of said regenerators (1) and carrying a portion of saidcleansed and cooled air back through said regenerators (1);

a heat exchanger communicative with said second conduit (4) through athird conduit (9) and with said column (5) by means of an air exitconduit (11) having an expansion valve (13) therein, said heat exchanger(10) further having countercurrent passages therein communicative with asource of higher pressure oxygen to be heated, said source including apump (20) communicative with the sump of said fractionating column (5)for pumping liquid therefrom to a pressure of between 40 and 300atmospheres absolute.

11. An apparatus in accordance with claim 10, further comprising acountercurrent heat exchanger (8), said first conduits (3) and said airexit conduit (11) passing through said countercurrent heat exchanger(8); and

expansion valves (3, 7) disposed in said exit conduit (11) and saidfirst conduits (3) between said countercurrent heat exchanger (8) andsaid column (5) for expanding fluids passing therethrough to thepressure of said column (5).

12. A process as defined by claim 1 wherein said raw air is compressedto a pressure of 9l2 atmospheres absolute.

13. A process as defined by claim 1 wherein said higher pressure is50200 atmospheres absolute.

14. A process as defined by claim 12 wherein said higher pressure is50-200 atmospheres absolute.

15. A process as defined by claim 1 wherein said column is operated at3-4 atmospheres absolute.

16. A process as defined by claim 14 wherein said column is operated at3-4 atmospheres absolute.

17. A process as defined by claim 1 wherein the branched portioncomprises 2030% of the entire cooled and cleansed raw air.

18. A process as defined by claim 8 wherein said process stream is at9-12 atmospheres absolute.

19. A process as defined by claim 1 wherein said higher pressure is50200atmospheres absolute.

20. A process as defined by claim 18 wherein said higher pressure is50200 atmospheres absolute.

21. A process as defined by claim 8 wherein a portion of oxygenwithdrawn from the sump of the fractionating column is branched offdownstream of the pumping Zone, and is recycled into said fractionatingcolumn.

References Cited UNITED STATES PATENTS 2,802,349 8/1957 Skaperdas 62l8XR 2,824,428 2/ 1958 Yendall 6241 XR 2,918,802 12/ 1959 Grunberg 6241 XR3,034,306 5/1962 Schuftan et al. 6241 XR 3,070,966 1/ 1963 Ruhemann eta1. 6239 XR 3,086,371 4/1963 Schilling 6241 XR 3,222,878 12/1965 Becker6241 XR 3,257,814 6/ 1966 Carbonell 6239 XR FOREIGN PATENTS 752,4391/1953 Germany.

WHrBUR BASCOMB, JR., Primary Examiner U.S. Cl. X.R. 6229, 39, 41

